My average score was 274 ms, so a bit over a quarter of a second. Which is as I understand it, a very average reaction time.
....Bit of a tangent here, but something to keep in mind though is that this is a very simplistic test and not necessarily indicative of your more "realistic" reaction time. In this test, you're waiting for a single and very simple stimulus (green square changing to a red square) and performing a simple action in response (clicking the mouse), and you know ahead of time what action you must take.
In Smash 4 it's sometimes argued that anything 15 frames (the game runs at 60 FPS, so that's a quarter of a second) or more is "reactable" given that's also roughly the average human reaction time (using that very same tester site as evidence lol)....but that's not necessarily true. An actual match is not so simple as that. You're fighting against another person and the two of you are doing so much more than waiting for a simple visual cue in a zero-stress environment. Sure, in 15 frames/a quarter of a second your brain may register "oh shit something's happening", but are you aware of what exactly it is they're doing? Once you are, you then have to select and execute the appropriate action in response. But by the time you have, ZSS has already grabbed you (with her frame 16 at earliest tether grab) and is Dthrowing you lol
Sometimes when it looks like a player reacted to something, they didn't, they were just anticipating it and so pre-emptively cut out some of the time spent/wasted figuring out what to do.
tl;dr: This test artificially makes your (or other peoples') reaction time seem better than it really is because you're not just purely reacting but rather anticipating a single, simple action and responding with a single, simple action.